This invention relates generally to a fluid sampling tool which, in response to pressure, opens to collect a fluid sample. The invention more particularly, but not by way of limitation, relates to a downhole well fluid sampling apparatus for use in a well, which apparatus does not open until a time delay after a pressure starts moving a valve of the apparatus.
In the oil and gas industry one from time to time needs to obtain one or more samples of fluid from a well bore. See U.S. Pat. No. 4,787,447 to Christensen, U.S. Pat. No. 4,766,955 to Petermann, U.S. Pat. No. 4,665,983 to Ringgenberg and U.S. Pat. No. 4,502,537 to Carter, Jr.
In general, to obtain a sample, a fluid sampling tool is first lowered, such as on a tubing string or a wireline or a slickline, into the well. When the tool is at the desired depth, a port (one or more openings) defined in the tool is opened, such as in response to pressure exerted through the well fluid or in response to an electrical actuation from the surface. The open port admits well fluid into a sample retaining chamber within the tool. The port is thereafter closed, the tool is withdrawn from the well, and the sample is taken from the chamber for analysis.
The fluid which one typically wants to analyze is fluid from a subterranean formation or reservoir intersected by the well so that it can be determined whether the fluid is suitable for being produced. It sometimes happens, however, that there is also drilling mud or other fluid in the well bore at or near the location where the well fluid sample is to be obtained. This latter, typically undesired (from a sampling standpoint) fluid can be the first fluid to be received by a fluid sampling tool, and it can be in sufficient quantity to fill the sample retaining chamber of the tool before any of the desired fluid can be stored. This produces an unwanted sample and slows or prevents the completion of the sampling process because one or more additional trips in and out of the well are needed to obtain a proper sample, if one can be obtained at all. This is, of course, costly. Therefore, there is the need for an improved fluid sampling tool which enhances the chances of obtaining a proper sample each time a sample is taken.
There is also a shortcoming with respect to the type of fluid sampling tool which uses shear pins to hold a valve adjacent the sampling port closed until a pressure in the well exceeds the holding force of the pins. Operation of such a tool at a desired depth requires that the holding force of the pins and the downhole pressure be accurately determined so that the two can be correlated to allow the tool to open at the desired depth. Making such an accurate determination of the holding force of specific pins and pressures at downhole locations can be difficult. Thus, there is also the need for an improved fluid sampling tool which has a reduced dependency on accurate pressure readings and shear pins.